This invention relates to braking systems for vehicles and more particularly to air brake systems for vehicles which have a plurality of braking devices and a plurality of separate controls which the operator may manipulate to initiate any of a plurality of different forms of braking.
Many vehicles have a plurality of sets of brakes, partly to provide the safety of redundancy and in part to enable selection of any of a number of different modes of braking. A wheel loader vehicle, for example, of the type having an elevatable bucket for scooping up and lifting bulk materials typically has a set of front wheel brakes, a set of rear wheel brakes and a parking and emergency brake. Such vehicles are often equipped with a first brake pedal or the like which applies the front and rear wheel brakes for slowing and precisely controlling vehicle motion and may also have a second brake pedal which, in addition to applying the front and rear brakes, temporarily establishes a neutral condition in the vehicle transmission to facilitate bringing the vehicle to a full stop. Still another control activates the parking and emergency brake which in air-operated systems is usually spring-biased to the engaged position so that it goes on automatically if control system pressure should be lost.
It has heretofore been the practice to provide some degree of redundancy or duplication of pneumatic circuit elements which control the brakes so that if a pressure loss occurs in one side of the system, from rupture of a hose or fitting or other cause, at least some of the normal selective braking capacity is retained. In braking systems of the kind outlined above, this duplication has not been as complete as would be desirable.
Considering another factor very significant to the reliability of an air brake system, the possibility of malfunction from pressure loss is related to the number of fittings and connections between scattered circuit components that are required in the system. In certain prior forms of air brake system, a number of the circuit components have been situated within a single housing assembly which arrangement has the effect of reducing the number of fittings and connections in the circuit. These prior arrangements do not provide the control functions required in a multimode braking system of the particular kind described above and are not readily susceptible to modifications to accommodate to the needs of such a system.